Under the 'Broadband & Calls' section of your account scroll to the bottom and in big letters it says 'Moving Home?', click the 'Find out how' button beneath it and the number pops up straight away in a large font, along with some basic instructions about the process. That number is 03300 412 462.
Have you perhaps got your broadband on a different Now account than your streaming?
Can you see any indication on the account you are looking at that you have Now Broadband?